The process of electroerosive wire-cutting generally makes use of a continuous wire electrode composed of, say, brass or copper, and having a thickness ranging between 0.05 and 0.5 mm. The wire electrode is axially transported continuously along a given continuous guide path from a supply to a takeup through a workpiece disposed in a predetermined cutting zone. The cutting zone is commonly defined by a pair of cutting guide members which support the wire electrode across the workpiece. Wire traction and braking means allow the continuous wire to be tightly stretched between the supply and takeup and to be axially driven between the cutting guide members while traversing the workpiece, thus presenting the continuously renewed electrode surface juxtaposed in a cutting relationship with the workpiece across a cutting gap. The cutting gap is flushed with a cutting liquid medium and electrically energized with a high-density electric current which is passed between the wire electrode and the workpiece to electroerosively remove material from the latter. The cutting process may be performed with any of various electroerosive machining arrangements. In electrical discharge machining (EDM), the cutting liquid medium is a dielectric liquid and the electric current is supplied in the form of a succession of electrical pulses. In electrochemical machining (ECM), the liquid medium is a liquid electrolyte and the machining current is a high-amperage continuous or pulsed current. In electrochemical-discharge machining (ECDM) the cutting medium has both electrolytic and dielectric natures and the machining current preferably is applied in the form of pulses which facilitate the production of electrical discharges through the liquid medium.
As the electroerosive material removal proceeds, the workpiece is displaced relative to the wire electrode transversely to the axis thereof. This allows the wire electrode to advance transversely to the workpiece and consequently a cutting slot to be formed behind the advancing wire electrode. The continuous relative displacement along a preselected path results in the formation of a desired contour corresponding thereto and defined by this cutting slot in the workpiece.
In performing the electroerosive wire-cutting process, the cutting zone is conveniently disposed in the air or usual environment and a nozzle is used to deliver the cutting liquid medium to the cutting gap. The cutting liquid is conveniently a water medium which may be ionized or deionized to various extents to serve as a desired electroerosive cutting medium. It is desirable to keep the cutting gap flushed with a sufficient volume of the cutting liquid and traversed thereby at a sufficient rate to allow the electroerosive action to continue with stability, the cutting chips and other gap products to be carried away with smoothness and the wire electrode to be cooled with effectiveness. This requires the cutting liquid to be projected under an elevated pressure. In the conventional arrangement in which the cutting zone or nozzle is exposed to the air, however, the cutting liquid, due to a pressure drop caused when it leaves the nozzle, tends to splash so that most of it flows out without coming into the narrow cutting gap spacing provided between the thin wire electrode and the workpiece. When the delivery of the cutting liquid to the cutting gap is insufficient or the cutting gap is incompletely filled with the cutting liquid, there develop gaseous discharges therein which impair the electroerosive process and removal of the gap products and eventually cause breakage of the wire electrode due to an excessive heat which then develop. An uncontrolled increase of the liquid pressure in an attempt to insure full delivery of the cutting liquid into the cutting gap will bring about an uncontrolled deflection or vibration of the wire electrode which again impairs the cutting stability. In short, there have been undue limitations of cutting stability and efficiency which accrue from the conventional gap flushing technique in the electroerosive wire-cutting process.